1. Field of the Invention
The present invention relates to a frame for a color picture tube, more specifically, to a frame for a color picture tube having an oxidized film formed thereon by plating zinc on a steel for a frame and calcinating, baking, sealing and exhausting of gas without an oxidizing process to overcome problems that occur by an oxidizing process and to manufacture by a simpler process.
2. Description of the Related Arts
After a shadow mask for color picture tubes (CPT) is assembled with a screen in a panel leaving a space between them, it is annealed for further processing and forming processes. The mask is finally formed by a press, and foreign substances such as oil, contaminants and fingerprints are removed by a next step, a degreasing process. The degreasing process is to remove oil and foreign substances used in the forming process by using original trichloroethylene solution. The formed shadow mask is fixed on a frame by welding to maintain the form thereof. For the frame to play a role of fixing the shadow mask, no changes of the form or outer size of the frame must be observed after calcinating for stability of an assembly against heat. The frame is assembled through springs which are attached by welding on the side faces of the frame. The frame and the degreased mask are electrically welded to produce a mask assembly and oxidized to prevent rust from forming. The oxidizing process is the process that forms an oxidized film of iron oxide (Fe.sub.3 0.sub.4) on the surface of the mask to protect from possible oxidation and diffused reflection such as thermal decalescence and exposure to light beams.
An oxidizing process is carried out according to the following oxidation reaction. ##STR1##
The oxidizing process proceeds by reactions (1) and (2) above 570.degree. C. and by reaction (3) below 570.degree. C. The steel used for such frames can form rust by oxidation before an oxidizing process, and an oxidized film produced with iron oxide (Fe.sub.3 0.sub.4 and FeO) is brittle and weak and clogs holes in the film. Therefore, the surface of the frame contains rust which can produce foreign materials before the oxidizing process and the total process is more complicated by an addition of an oxidizing process.
Japanese Patent 89-1522044 discloses a process for a color picture tube solving the above problem of the conventional arts. After Ni and Cr are plated on a shadowmask, frame and inner shield at a thickness of 0.5 .mu. to 1.0 .mu., the shadowmask and the frame are welded to produce a maskframe. The frame and a holder are attached, and the maskframe and a panel are assembled. Then the fluorescent screen is formed, and an oxidized film of metal components is formed using sealing, exhausting and aging processes. The surface of the metal formed by a thermal process and not an oxidizing process is thinner and harder than the conventional oxidized film.